This invention relates to seals, and, more particularly, to a brush seal for a rotary machine.
Rotary machines include, without limitation, turbines for steam turbines and compressors and turbines for gas turbines. A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas-path leakage in the turbine or compressor area of a gas turbine, between the rotor of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
Annular brush seals have been used, or proposed for use, between a rotor and a surrounding casing (i.e., stator casing) in gas and steam turbines. A gas or steam turbine brush seal is made up of circumferentially-arrayed brush seal segments. Each brush seal segment includes a plurality of flexible, metal-wire bristles attached to (e.g., welded to) a metal bristle holder which has a shape of an annular segment of a circular ring. The bristle holder has a fixed radius and a fixed circumferential length corresponding to the radius and circumferential length of the surface groove of the annular casing segment into which the bristle holder, with attached bristles, is inserted. The bristle holder may include a backing plate positioned between the bristles and the lower-pressure side of the seal with the free ends of the bristles radially-inwardly-extending beyond the radially-inward end of the backing plate.